In medical non-invasive therapy system in particular radiotherapy systems, such as conventional linear accelerators or MR Linac systems, the patient anatomy being treated or imaged should be aligned with the radiation isocentre as accurate as possible for each and every set up and each treatment fraction. One source of potential inaccuracy in the alignment is the repositioning of the bed on which the patient rests. As many medical radiotherapy systems require the patient to be placed into an enclosed and confined space, hereinafter called treatment bore, the patient must be set up for treatment outside the treatment bore and then transported into the treatment bore for the medical treatment to begin. Therefore, the bed must be movable between these two locations and positionable to a high degree of accuracy as misalignment during set up may entail that the patient will need to be removed from the medical radiotherapy system and realigned before treatment can commence, and thus wasting time and resources.
It is also of very high importance that the patient positioning is as stable as possible during the movement as well during the treatment or imaging. Hence, the position of the bed in treatment bore in the medical radiotherapy system must be very stable. The process of moving the bed from its support outside the medical radiotherapy system into the treatment bore inside the medical radiotherapy system itself requires careful alignment with the treatment table of the system as well as a high degree of stability.
Furthermore, it is also important that the patient set up and of moving the bed from its support outside the medical radiotherapy system into the treatment space inside the medical radiotherapy system is secure for the patient and easy to handle for the medical staff. The risk of patient injuries must be minimized during movement as well as during treatment in order to provide as high patient security as possible and minimize risk for patient movements during treatment.
Moreover, in medical non-invasive therapy systems, in particular in MR Linac systems, it is of very high importance that all material in the treatment bore or treatment volume is known and taken into account in the planning system. As all material will absorb radiation dose, it is important to reduce the material present in the treatment bore as much as possible and it is also important that the positions of material structures are known. In addition it is important to know the distribution of the material and further to ensure that the material does absorb as little magnetism and radiation as possible in order to provide good quality images with the magnetic resonance imaging system and to predict the dose of radiation that reaches the patient and the target tissue/position in or on the patient, respectively.
An additional requirement is that the material used for structural components and in particular for spring or elastic applications remains stable and keeps its characteristics even when exposed continuously to radiation. In particular plastic changes its characteristics when exposed to radiation over time; it gets brittle when exposed to radiation. The brittleness increases the risk of structural components breaking when exposed to deforming stress, which spring elements or other elastic elements usually are exposed to.
In summary, there is a number of important factors to take into account when designing structural elements for use in medical radiotherapy systems and/or magnetic resonance imaging systems or a combination of the two, such as MR Linac systems.